1. Field of the Invention
The present invention relates to an aqueous dispersed solution as a standard solution for determining the content of lipids, and a process for producing the same.
2. Description of the Prior Art
Determination of lipid levels in a body fluid, particularly determination of cholesterol levels, has rapidly come into wide use with the recent development of an enzymatic determination process, and its utility in the field of clinical diagnosis has been increasing. Therefore, a proper standard solution for determination of lipid levels is required. However, it is essentially difficult to dissolve lipids in water and, therefore, those dissolved in an organic solvent are exclusively used. For this, the lipid in these standard solutions differs in the existing state and fluid property from the lipid in the humor such as serum. This causes a great difference in reactivity between the standard solution and the body fluid (e.g., serum) as a specimen, which results in error in determined value.
Therefore, human- or animal-derived serum or purified lipoprotein cholesterol has been used as the standard solution. The process for purifying lipoprotein cholesterol is described, for example, in Japanese Laid-Open Patent Publication No. 56-101555. However, in the process using sera, it is difficult to obtain sera at a cheap price and, at the same time, there is a fear of an influence of unknown impurities on the determined value. The process for purifying lipoproteins has also a problem of complexity.
In order to improve these drawbacks, those which are solubilized in water with a surfactant have been used as the standard solution. However, a large amount of the surfactant is required for the solubilization of lipids in water. Therefore, the viscosity of the solution prepared by this process becomes high and its handling is sometimes difficult.
In order to solve this problem, it is suggested to use a mixture of a surfactant and lipids, which are different in HLB value (e.g., Japanese Laid-Open Patent Publication No. 57-84356). However, regarding the solution obtained by this process, the enzymatic reaction is sometimes inhibited by the surfactant present in the solution in the above enzymatic determination process. Since the lipid dispersion form is different from that in serum, the solution is not sometimes suitable as the standard solution according to the determination process.
As described above, various processes for stably dissolving or dispersing lipids in a simple procedure have been studied.
However, the fact that the dispersion form of lipids is largely different from that in serum as described above sometimes becomes a problem which hinders the use of the solution as the standard solution for calibrating a device. Taking this point into consideration, a process for dispersing lipids using the surfactant is also used. However, there is a problem that a high concentration of cholesterol, which is generated physiologically, can not be dispersed stably when a surfactant may be used.